Zirconium-hafnium alloys for coinage



United States Patet 3,373,617 Patented Mar. 12, 1968 ice 3,373,017 ZERQONIUM-HAFNIUM ALLOYS FOR 'COINAGE Donald R. Spink, East Amherst, and William W. Stephens, Williamsville, N.Y., assignors to Amax Specialty Metals, Inc., Akron, N.Y., a corporation of Delaware No Drawing. Filed Mar. 29, 1965, Ser. No. 443,620 4 Claims. (Cl. 75177) This invention relates to an alloy for use as a coinage metal, and more particularly to a zirconium-hafnium alloy wherein the hafnium is present in an amount greater than that normally occurring in nature, and to a method of forming said alloy and coining said alloy.

A coinage metal alloy should have good wear characteristics, malleability for ease of forming into coins, and beauty. In this connection, silver has long been used as the principal coinage metal of the world. It possesses a beauty, wear characteristics and malleability to make it a good coinage metal. In recent years, however, industrial use of silver has sharply increased, thus placing a strain on the limited supply of silver available which has caused a corresponding increase in the price of silver because of the heavy demand for the metal. This trend has caused many nations of the world to eliminate the use of silver as a coinage metal or, as an alternative, to decrease the amount of silver used in the coinage alloy. These steps have been necessary since the value of the silver in coins has risen until at present, the value of the silver in the coin has become equal to or almost equal to the value that the coin represents. This situation has led to the hoarding of coins, either for speculation or for subsequent extraction of silver in the coin for other purposes, with the result that a serious coin shortage has developed.

Many proposals have been set forth in an attempt to overcome the problems caused by the use of silver as a coinage metal. Among such proposals set forth to eliminate the coin shortage is the suggestion that coins be produced from nickel or aluminum alloys in place of the silver currently used as a coinage alloy. This proposal has numerous drawbacks, the most outstanding of which is that reducing or eliminating the silver in the coin is an open invitation to counterfeiters to duplicate the alloy used in the coin, especially if the substitute metal is or will be readily available in normal channels of commerce.

Counterfeiters, by using modern electro forming techniques, are readily able to reproduce the dies used to strike the coins; however, their activities in the past have been restricted due to the high silver content of the alloy used in the coin. The expense of this alloy made counterfeiting unprofitable and attempts to use other alloys in counterfeit coins met with very little success, since the physical properties of the counterfeit alloys used were difierent from the silver alloy, thus makin coins produced therefrom readily detectable. However, decreasing or eliminating the silver from the coin makes it easier for a counterfeiter to duplicate the alloy of the coin. Furthermore, replacement of silver alloys in coins with nickel or aluminum alloys or other readily available metal alloys makes it possible for a counterfeiter to duplicate the coin alloy with very little difficulty or expense. It can be Seen therefore, that although it has become nece sary to avoid the use of silver in coins, there is a need for an alloy having the beauty, wear characteristics and malleability of silver alloys, but which at the same time is very difficult to counterfeit.

Accordingly, it is an object of this invention to provide a coinage alloy which eliminates the use of silver.

it is an object of this invention to provide a coinage metal having the beauty, malleability and wear characteristics consistent with its use as a coinage metal.

It is a further object to provide a coinage alloy that is virtually impossible to counterfeit.

Various other objects and advantages will appear from the following description of the invention, and the novel features thereof will be particularly pointed out hereinafter in connection with the appended claims.

The unique coinage metal alloy of this invention comprises a zirconium-hafnium alloy wherein the hafnium is present in an amount greater than the amount of hafnium normally occurring in zirconium ore.

Zirconium and hafnium are always found together in the natural state because of the chemical similarity of the two metals. The amount of hafnium naturally associated with zirconium generally ranges around 2 wt. percent of the zirconium-hafnium content of the ore, however some substantial deposits of zirconium ore have been found having a hafnium content in the range of 7 to 8 wt. percent. Because of the chemical similarity of zirconium and hafnium it is extremely difficult to alter the content of the hafnium in the ore and thus produce an alloy having a hafnium content different from the hafnium content of the starting ore. It is estimated that an investment of several millions of dollars would be required to acquire the equipment necessary to produce zirconium-hafnium coinage alloy where the content of the hafnium is greater than that normally associated in zirconium ore. In other words by setting the hafnium content of the coinage alloy high, above 8.5 wt. percent of the alloy, it is made economically impossible for a counterfeiter to attempt to duplicate the alloy of the coin, since a large investment in equipment is necessary in order to be able to do this.

In a preferred embodiment of this invention, the zirconium-hafnium alloy has a hafnium content of 10 wt. percent to 12 wt. percent of the alloy. This hafnium content is chosen because it is far above the highest known hafnium content in naturally occurring ores and thus, any accidental duplication of the coinage alloy of this invention is avoided. In order to further prevent counterfeiting it is entirely possible to provide alloys of differing hafnium content for coins of different denominations. For example a coin worth 25 cents might be produced from a zirconium-hafnium alloy wherein the hafnium content is 10 wt. percent and a coin worth 50 cents might be produced from a similar alloy having a hafnium content of 20 wt. percent.

Zirconium has the further advantage of being widely distributed in nature and being in plentiful supply. While zirconium is not one of the most abundant elements, it does rank eleventh in the list of elements in the earths crust. The zirconium content of the earths crust is estimated to be more than 0.028 percent, which is more than the common metals such as copper, lead, nickel and zinc. For example there is more than three times as much zirconium in the earths crust as there is nickel. Thus, there is an abundant and widely distributed supply of zirconium for use in coins.

The inventive zirconium-hafnium alloys have the beauty of silver and look and feel very similar to the silver alloys currently in use. This would enhance its acceptance by the general public, as contrasted with the distrust of the steel and aluminum coins which have been tried in the past.

The inventive zirconium-hafnium alloys are easily cold formed, and it would require little or no change in minting procedures or equipment to produce coins from such alloys.

In order to illustrate a preferred embodiment of this invention, the following example is given.

Example I Zirconium-hafnium ore containing, for example, about 2 wt. percent hafnium based on the ore is decomposed by heating the ore in an electric arc furnace, in the presence of carbon, above 3000 C. to form zirconium-hafnium carbo-nitride. The carbo-nitride is chlorinated to form zirconium-hafnium tetrachloride. The tetrachloride is then dissolved in Water to form zirconium-hafnium oxychloride. The oxychloride solution is complexed with ammonium thiocyanate and is subjected to a liquid-liquid extraction process wherein sufficient zirconium is removed from the complex to bring the hafnium content up to wt. percent based on the Zirconium content of said complex. The zirconium-hafnium enriched complex is precipitated from solution, filtered, and ignited to form zirconia and hafnia. The zirconia enriched-hafnia portion is then rechlorinated to form the tetrachloride of zirconium and hafnium which is subsequently reduced with magnesium to form a sponge of zirconium-hafnium metal, the hafnium content being 10 wt. percent of the zirconiumhafnium content. The sponge so produced is formed into a consumable electrode which is melted under vacuum, in an electric furnace to form an ingot. The ingot is forged into a slab and the slab is conditioned to remove scale by blasting and pickling. The slab is then hot rolled into a sheet having a thickness between 0.10 and 0.75 of an inch, and the operation is completed by cold rolling the sheet to final gauge. The cold rolled sheet is pickled and annealed.

It is preferable to enrich the ore by the method shown above, rather than to start with pure zirconium metal and add the desired amount of hafnium, because the alloy formed according to the method shown above is of a more uniform composition and is presently the most economical method of producing a zirconium-hafnium alloy wherein the hafnium content is enriched.

Example II An alloy consisting essentially of zirconium and hafnium, the hafnium content being 12 wt. percent of the alloy can be made in the same manner as in Example I. Coins are made from sheets of this alloy by essentially the same method as currently used in producing silver alloy coins: i.e., blanking slugs from the alloy sheet; edge rolling the slugs; and coining the slugs by forming a design on the face of the coin by means of a die. It may be preferred, however, to include a short annealing period after edge rolling the slug in order to relieve internal stress in the slug. This step is carried out at a temperature between 1200" F. and 1300 F., under vacuum or in an inert atmosphere.

As can be seen from the above examples, it is essential that the alloy used in the coin be sufiiciently malleable to lend itself readily to the cold forming operations involved in producing the coin. It is a feature of the present invention that the zirconium-hafnium alloys thereof are duetile and can be cold formed with ease.

The alloys of the present invention produce a coinage metal having a silvery-White appearance, similar to a silver alloy. Coins struck from these alloys have a feel similar to coins currently in use, and when dropped on a hard surface emit the characteristic ring of silver coins. These alloys are resistant to strong boiling acids and the molten alkalies and have wear characteristics superior to the silver alloy currently in use for the production of coins.

While the invention has been described in terms of the present preferred embodiments, it should be understood that it may be otherwise embodied within the scope of the following claims.

We claim:

1. Coins having a silvery-white appearance, a feel and a characteristic ring when dropped similar to high silver content coins and having wear characteristics at least equal to such silver coins consisting essentially of an alloy of zirconium and hafnium, said hafnium being present in an amount greater than 8.5 weight percent of said alloy.

2. Coins as set forth in claim 1, wherein said hafnium is present in an amount of from 8.5 to 20 weight percent of said alloy.

3. Coins as set forth in claim 2, wherein said hafnium is present in an amount of from 10 to 12 weight percent of said alloy.

4. A method of forming a zirconium-hafnium alloy suitable for use as a coinage metal which comprises:

(a) decomposing a zirconium-hafnium containing ore so as to form zirconium and hafnium oxychloride;

(h) enriching the hafnium content of said oxychlorides by complexing with ammonium thiocyanate and extracting from said complex sufiicient zirconium so that the hafnium content in a remaining portion is greater than 8.5 wt. percent of the zirconium in said remaining portion;

(c) igniting said remaining portion so that said Zirconium and hafnium complex is converted to zirconia and hafnia;

(d) chlorinating said ignited remaining portion so that said zirconia and hafnia contained therein are converted into zirconium tetrachloride and hafnium tetrachloride;

(e) reducing said chlorinated remaining portion with magnesium so that zirconium-hafnium metal sponge is formed, said metal sponge having a hafnium content greater than 8.5 wt. percent of the zirconium contained therein;

(f) forming the sponge into a consumable electrode;

(g) decomposing said consumable electrode in an electric furnace under vacuum to form an ingot;

(h) forging said ingot into a slab;

(i) conditioning said slab by blasting and pickling so that scale is removed from said slab;

(j) hot rolling said conditioned slab into sheet having a thickness of around A to of an inch;

(k) cold rolling said sheet to final thickness; and

(l) pickling and annealing said cold rolled sheet.

OTHER REFERENCES Zirconium and Hafnium, U.S.I. Industrial Chemicals Company, 1957, p. 10.

DAVID L. RECK, Primary Examiner,

SAITO, Assis ant E am ner. 

1. COINS HAVING A SILVERY-WHITE APPEARANCE, A FEEL AND A CHARACTERISTIC RING WHEN DROPPED SIMILAR TO HIGH SILVER CONTENT COINS AND HAVING WEAR CHARACTERISTICS AT LEAST EQUAL TO SUCH SILVER COINS CONSISTING ESSENTAILLY OF AN ALLOY OF ZIRCONIUM AND HAFNIUM, SAID HAFNIUM BEING PRESENT IN AN AMOUNT GREATER THAN 8.5 WEIGHT PRECENT OF SAID ALLOY. 